I am not aware or any reaction between kingspan and PVC cable that will cause the cable to become brittle (unlike the reaction between expanded polystyrene and PVC cable).

If you put the cables behind the kingspan then you are at risk of lowering the current carrying capacity (CCC) and may cause the cable to overheat. This is not applicable to the lighting circuit if using 1.5mm T&E but it may be important for the socket circuits.

Putting the cable in conduit also lowers the CCC and could make things worse.

I'll get back later as I am off to work and I have really been looking forward to working this Saturday.........

OnlyMe wrote:I am not aware or any reaction between kingspan and PVC cable that will cause the cable to become brittle (unlike the reaction between expanded polystyrene and PVC cable).

If you put the cables behind the kingspan then you are at risk of lowering the current carrying capacity (CCC) and may cause the cable to overheat. This is not applicable to the lighting circuit if using 1.5mm T&E but it may be important for the socket circuits.

Putting the cable in conduit also lowers the CCC and could make things worse.

I'll get back later as I am off to work and I have really been looking forward to working this Saturday.........

Haha I feel for you, but thanks for the help.

I imagine there will be a void of about 3-4cm between the Kingspan (or whatever insulation board that isn't polystyrene that I can get my hands on)

Not entirely sure how back boxes etc get fit, assuming they'd have to cut out a chunk of the insulation board so it fits.

That is the other problem with taking the cables behind the kinspan and not in front of it. You have to puncture the kingspan and pass the cables through it. This again will effect the cables CCC and the integrity of your insulation. Is there anyway you can just fetch the cables down the front of the kingspan?

BTW work was a blast. Nearly 2 hours to get through security, two level B rub downs and a complete search of the van - a massive argument about what was and not allowed (including the ladders on the roof, a can of deicer and an orange hi viz vest that she found )

OnlyMe wrote:That is the other problem with taking the cables behind the kinspan and not in front of it. You have to puncture the kingspan and pass the cables through it. This again will effect the cables CCC and the integrity of your insulation. Is there anyway you can just fetch the cables down the front of the kingspan?

BTW work was a blast. Nearly 2 hours to get through security, two level B rub downs and a complete search of the van - a massive argument about what was and not allowed (including the ladders on the roof, a can of deicer and an orange hi viz vest that she found )

I should be able to get them between the insulation and plasterboard. I reckon I'll have a 2-3cm gap where they can run.

Do they have the go in conduit? As I can't exactly clip them to the insulation without piercing it

You can attach the cables to the kingspan with self adhesive cable clips or gaffer tape.

When I said puncturing the kingspan I meant a hole right through it! That's not the same thing as piercing it with a cable clip (and normal cable clips will not hold onto kingspan).

If you are using dry liner boxes (usually 35mm deep) then you will have a 12.5mm plasterboard plus whatever gap between the plasterboard and the kingspan. If the gap is not big enough then you are allowed to scrape into the surface of the kingspan, just do not go all the way through it.